Transesophageal echocardiography (TEE) is an ultrasound imaging technique that provides images of the heart for diagnostic and/or monitoring purposes. One particularly beneficial use of TEE is for obtaining images of the transgastric short axis view (TGSAV) of the left ventricle. To obtain the best images of the TGSAV using TEE, the ultrasound transducer should ideally be positioned in the fundus of the stomach, with the ultrasound beam aimed through the left ventricle.
TEE probes for imaging the TGSAV typically contain mechanical articulation mechanisms to bend the distal end the probe into the desired position in the fundus. Since conventional TEE probes are relatively large (i.e., on the order of ½ inch in diameter), the articulation mechanisms can be relatively strong. As a result, when the probe is not perfectly aligned with the desired position, the probe can exert significant forces on the relevant anatomical structures to push the distal end of the probe into the desired location for obtaining the TGSAV. However, when smaller TEE probes are used (e.g., the 5 or 6 mm diameter probes described in U.S. patent application Ser. No. 10/996,816), the probe may not be able to exert enough force to push the distal end of the probe into the desired location.
U.S. application Ser. No. 10/996,816, incorporated herein by reference, discloses a TEE probe for use in adults that is preferably less than 7.5 mm in diameter, more preferably less than 6 mm in diameter, and most preferably about 5 mm in diameter. It also discloses a pediatric TEE probe that is preferably between about 2.5 and 4 mm in diameter.
To obtain the best images of the TGSAV, the ultrasound transducer (which is located in the distal end of the probe) should be positioned in the fundus of the stomach, pressed up against the mucosa. The optimal position of the transducer within the fundus depends on a number of parameters including the size of the heart and the position of the heart relative to the fundus. These parameters may vary, for example, with body size, body habitus, and/or anatomical relationships. The optimum position for the transducer within the fundus is referred to hereinafter as “OPF”.
To get the transducer at or near the OPF to perform imaging, the distal end of the probe is inserted in its unbent position into the patient's nose or mouth, down through the patient's esophagus, and into the fundus of the stomach. After the tip of the probe has been inserted to the appropriate depth, the operator (e.g., a doctor) actuates an articulation mechanism to bend the distal end of the probe until it comes into contact with the mucosa lining the superior portion of the fundus, preferably positioning the distal end of the probe at an acceptable position or, most preferably, at the OPF. Once the distal end of the probe is at a position, ultrasound images can be obtained. If, based on the images, it is determined that the distal end is not at an acceptable position or the OPF, the position of the probe may be adjusted to improve the images.
The entrance from the esophagus to the stomach is called the lower esophageal sphincter. The lower esophageal sphincter is a relatively stable area because the esophagus itself has a thicker musculature at this point and because the area is supported where it passes through the diaphragm. If the distance from the lower esophageal sphincter to the OPF was the same in all patients, a probe could be designed with its bending joint located at a corresponding distance from the distal tip of the probe. In practice, however, the distance between the lower esophageal sphincter and the OPF (referred to hereinafter as “LOD”) varies from patient to patient. For example, the LOD may typically be between 4-10 cm in adults, and 2-5 cm in children, depending upon body size, body habitus and the position of the heart relative to the diaphragm.
Conventional large TEE probes (e.g., ½ inch in diameter) have a bending point that is located at a fixed distance from the distal tip of the probe, and can exert significant forces on the relevant anatomical structures to push the distal end of the probe into a suitable location for obtaining the TGSAV. However, the operator of the device may not perceive the forces as being high due to the mechanical advantage provided by the articulation controls. The distal tip positioning of conventional probes is accomplished by deflecting the relatively compliant lower esophagus and upper stomach cavity with a stiff probe insertion tube and by a powerful bending section within the probe. However, when smaller TEE probes are used, the probe will often be unable to exert enough force to push the distal end of the probe into a suitable location. Examples of smaller TEE probes include TEE probes for adults that are less than 7.5 mm in diameter, and pediatric TEE probes that are preferably less than 4 mm in diameter (as described in U.S. application Ser. No. 10/996,816).